CHEK1 and neoplasm: Checkpoint kinase 1 (Chk1) which encoded by CHEK1 gene trigger cell cycle arrest upon DNA damage [21] Although CHEK1 was initially thought to be a tumor suppressor gene due to its role in checkpoint activation and cell cycle arrest, several studies documented a positive correlation between Chk1 expression and tumor grade and disease recurrence, suggesting that Chk1 may promote tumor growth [22–24].